낙동강 수계 용존 유기물질의 기원, 특성 및 거동

Abstract

The Nakdong River is the primary source of drinking water for southeastern part of korea. Therefore many effort and investment have been given the Nokdong River watershed to improve water quality since the 1980s. However, organic contaminants level measured as BOD and COD has not been reduced during the last 10 years, and even increased at some part of river depending on the season and the location. Discharge of treated w.w and agricultural runoff into river can change the composition of DOM by increasing the loading of biologically drived DOM or increasing nutrient loading and thus promote enhanced seasonal algae blooms. Recently, it has been realized that BOD and COD as an index of organic matter have some limitation on the management of the Nakdong River water quality. Therefore, an alternative index of organic matter are needed to estimate the organic matter concentration and composition. One of the Key issues in watershed management for DOM control is an understanding of the origin and genesis of aquatic organic matter. The nature and properties of dissolved organic matter (DOM) in water are topics of significant environmental interest, because it is a major reactant in and product of biogeochemical processes in the watershed. However, DOM concentration, composition, and chemistry are highly variable and depend on the sources of organic matter (ex, allochthonous vs. autochthonous); on the temperature; on the surface chemistry of sediment and soil; and on the presence of photolytic and microbiological degradation processes. Therefore, it is very necessary to characterize DOM for understanding and predicting the fate of DOM or its fraction in specific environment. Dut to the complex nature of DOM, a variety of experimental methods were used to characterize it. The methods include DOM fractionation using XAD resins, UV absorbance, Fourier Transform Infrared (FTIR) spectroscopy, fluorescence spectroscopy, and size exclusion gel chromatography which were also used in this work. The main objective of the study described here was to assess the contribution of point sources to the DOM loading into the Nakdong River. Other specific objectives were to assess DOM concentrations, composition, and properties of waters, to identify origins and sources of DOM, estimate DOM input to the Nakdong River, determine the effects of the point source DOM on the Nakdong River water quality, and determine seasonal and flow effects on DOM composition. These data can be used to evaluate the effectiveness of watershed best management practices at ensuring of the Nakdong River. In order to understand the spatial and temporal changes in DOM in rivers and lakes, more information on the origin of the different organic compounds must be gathered. The chemical composition of surface waters reflects the nature of their catchment. Therefore, DOM sources on the catchment have to be taken into account. The Nakdong River samples collected on 9 different sites from 2011, Aug. to 2012, Nov. had different DOM fractionation. DOM in all of the water samples exhibits a heterogeneous matrix of organic components having different fraction patterns. These differences in DOM fractionation patterns demonstrate the dynamic nature of DOC concentration and composition changes as a function of environment, flow, and season. Also, the results of this study indicate a number of unusual features of Nakdong River watershed in regard to its DOM characteristics and this information will help in the management of refractory organic matter later in Nakdong River and Namgang Lake. This work also have characterized DOM in several wastewater treatment plant effluents. The DOM fractionation was also substantially different with respect to water sources and treatment precesses. In addition, DOM sampled from several organic sources was fractionated and measured with DOC, UV absorbance, FTIR, fluorescence, and molecular weight, etc. This result showed that some distinct characteristics are associated with the organic source. The characteristics of DOM collected from different sources were markedly different from source to source and seasonally. For this research, organic matters were isolated from 9 samples selected for natural or engineered bioactivity: river sample, treated w.w., mountain stream, pond, plant litter, soil etc. The isolated organic matters were characteriged by multiple advanced techniques including ion exchange resins. Forier trandform infrared spectroscopy, fluororecence spectroscope. For example, the DOM fractionation of the soil and leaves differs from the DOM fractionation of water samples. And, the terrestrial organics (sediments from wetland and river and soil from rice pod) are composed of a relatively high amount of hydrophobic above 55 % and of polysaccharide-like substances. The properties of DOM were also affected by seasonal variations, especially for surface waters. In addition, triangle analysis based on the various sources of DOM reveals that the property of DOM in the mainstream of the Nakdong River was very similar with the DOM source from wastewater treatment plants. Even though presently we can not make clear interpretation of DOM fractionation data obtained from this study, these data will be used as a fingerprint after collecting more data from continuing future works.